Attic Knee Wall Construction

What are knee walls.

Attic knee wall construction.

The higher the knee wall the greater the amount of useful wall space you create in your finished attic. A knee wall is a short vertical wall roughly two or three feet high that blocks in that useless triangular space. Support and follow me. You can see the image below for an example of a knee wall.

But you do so at the expense of floor space. Knee walls are short usually wooden walls installed around the sides of an attic where the rafters meet the floor. The bottom plate of the knee wall rests on top of the floor joists leaving a large pathway for attic air to come up into the air cavity of the knee wall. In most instances they are no taller than 3 feet but some builders may custom fit them according to the roof s shape and size.

If you aren t sure whether or not your attic contains knee walls go and look around the edges. The knee wall will be built on the floor of the attic and then tipped into place against the rafters. Install insulation without misalignments compressions gaps or voids in all knee wall cavities. Install a top and bottom plate or blocking at the top and bottom of all knee wall cavities.

One of your 2x4s will act as the bottom of your wall and will not be cut. Scribe a line on your scrap piece along the angle formed by the rafter. Determine the angle of rafters by setting the scrap piece of 2x4 in a vertical position against the side of a rafter. Framing basics for attic knee walls along the sides of your loft or attic space.

Secondly without an air barrier on the back of the knee wall and with the potential to sag as indicated above attic air goes around the insulation into the cavity on the vertical space as well.